<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>isNil</title>
</head>

<body>
    <script>
        const isNil = val => val === undefined || val === null;
        document.write(`isNil(null)的结果是:${isNil(null)}`)
    </script>
</body>

</html>